vfsx21.patch available - vfs work (expert developers only)

Oops, here's another update, right after the vfsx20 update :-).
I had to revert to LK_SHARED locks to LK_EXCLUSIVE due to some
UFS braindamage in its directory scanning code which was causing
some memory corruption.
fetch http://leaf.dragonflybsd.org/~dillon/vfsx21.patch
I will eventually fix the UFS directory scanning code, but not in
the current patch set.
-Matt